JP3143859B2 - Method for producing nuclear fuel granules using insoluble tannin - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing nuclear fuel granules by adsorbing nuclear fuel materials such as uranium and thorium onto insoluble tannins.

[0002]

2. Description of the Related Art Conventionally, nuclear fuel substances such as uranium and thorium in radioactive waste liquid have been adsorbed on insoluble tannins, and the insoluble tannins have been incinerated to form oxides of the nuclear fuel substances, which are reused as nuclear fuel. (Japanese Patent Laid-Open Publication No. Hei 3-206094).

[0003]

However, when the insoluble tannin is brought into contact with the aqueous solution containing the nuclear fuel substance in order to cause the nuclear fuel substance to be adsorbed on the insoluble tannin, the insoluble tannin swells and becomes very bulky. Becomes larger. Because the water content of the swollen insoluble tannin is high,
Attempts to incinerate in this state consume a large amount of heat energy, and also complicate temperature management.
In addition, since the uranium concentration in radioactive waste liquid is generally as low as several hundred ppb, when radioactive waste liquid is used as a starting material to produce nuclear fuel by the above method, a large amount of insoluble tannin and a long adsorption time are required, and the production efficiency is low. There was a very poor disadvantage. The insoluble tannin has a particle size distribution of several μm to several mm, and when a nuclear fuel substance is adsorbed on the insoluble tannin of several μm and incinerated, several μm
m of fine nuclear fuel is obtained. In the case of producing pellets or packed nuclear fuel using this fine powder nuclear fuel,
There was a problem that nuclear fuel in the form of fine powder was scattered during the production of pellet or packed nuclear fuel. An object of the present invention is to provide a method for efficiently producing nuclear fuel granules with small energy consumption without being scattered as fine powder when producing pellets or packed nuclear fuel using nuclear fuel granules. It is in.

[0004]

The invention according to claim 1 is
An aqueous solution containing a nuclear fuel substance is brought into contact with an insoluble tannin to cause the nuclear fuel substance to be adsorbed to the insoluble tannin, and then the nuclear fuel substance is adsorbed on the insoluble tannin. Is 0.01 to 5 mm, the aqueous solution contains 1 to 10% by weight of the nuclear fuel material, and the insoluble tannin to which the nuclear fuel material is adsorbed is subjected to compression dehydration, and then dried at a temperature from room temperature to 400 ° C. A method for producing nuclear fuel granules using insoluble tannin, comprising roasting insoluble tannin in an oxidizing atmosphere or a non-oxidizing atmosphere at a temperature of 400 to 2000 ° C.

[0005] When the insoluble tannin to which the nuclear fuel material is adsorbed is roasted, the insoluble tannin is burned off and only the nuclear fuel material is obtained. Since the insoluble tannin has a particle size of 0.01 to 5 mm, the nuclear fuel after roasting becomes granular, and there is no possibility of scattering as a fine powder during the production of pellets or packed nuclear fuel later. If the particle size of the insoluble tannin is less than 0.01 mm, scattering is likely to occur, and insoluble tannin having a particle size exceeding 5 mm is not easily available. In addition, since the insoluble tannin to which the nuclear fuel material is adsorbed is compressed and dehydrated before baking and dried at a predetermined temperature, the water content of the insoluble tannin swollen without eluting the nuclear fuel material adsorbed to the insoluble tannin is reduced, and drying and Energy consumption required for roasting can be greatly reduced. In addition, temperature control for drying and roasting becomes easy. By adjusting the concentration of the nuclear fuel substance in the aqueous solution to 1 to 10% by weight, a relatively small amount of insoluble tannin is required, and the nuclear fuel substance can be efficiently adsorbed to the insoluble tannin in a short adsorption time.

The invention according to claim 2 is the invention according to claim 1, wherein the aqueous solution containing the nuclear fuel substance has a uranium concentration of 1
This is a method in which an aqueous solution of a uranium compound is 10 to 10% by weight, and the pH of the aqueous solution is 3 to 4. If the uranium concentration is less than 1% by weight, the amount of waste liquid after adsorbing uranium becomes too large, and if it exceeds 10% by weight, it is difficult to adsorb all uranium to insoluble tannin, and uranium remains in the waste liquid. , Respectively, is not preferred. Further, when the pH of the aqueous solution containing uranium is less than 3, the uranium adsorption rate to insoluble tannin is significantly reduced, and when the pH exceeds 4, precipitation occurs in the aqueous solution, which is not preferable.

A third aspect of the present invention is the method according to the first or second aspect, wherein the dried insoluble tannin is roasted at a temperature of 400 to 800 ° C. in an oxidizing atmosphere.
This method is a method of producing nuclear fuel granules in the form of an oxide for making pellets. When an oxide is used, the insoluble tannin after drying is roasted in an oxidizing atmosphere, that is, in the air or oxygen. As a result, only the tannin component is removed by combustion, and the adsorbed nuclear fuel material such as uranium is converted into an oxide and forms loosely aggregated particles. 40
In the roasting in the range of 0 to 800 ° C., the particles are not unnecessarily sintered, and thus can be formed into a pellet shape as it is. By sintering the pellets, the same nuclear fuel as that conventionally used in nuclear reactors can be obtained. At a temperature lower than 400 ° C., it takes a long time to roast the tannin component, or the tannin component is not completely roasted, and many impurities such as carbon remain. If the temperature exceeds 800 ° C., the sintering of the particles proceeds, and if it is sintered, it cannot be used as a raw material for pellets, and thus requires pulverization. There is a problem that fine powder is generated during pulverization.

The invention according to claim 4 is the invention according to claim 1 or 2, which is a method of roasting dried insoluble tannin at a temperature of 800 to 1800 ° C. in an oxidizing atmosphere. This method is a method of producing nuclear fuel granules in the form of an oxide for producing a filled nuclear fuel. At a temperature of 800 ° C. or higher, the sintering of the particles proceeds, and the particles have a high tap density. Therefore, the particles can be directly filled in a metal tube to be used as a nuclear fuel. If the temperature is lower than 800 ° C., sintering of the particles does not occur and a desired tap density cannot be obtained. Even if roasting is performed at a temperature exceeding 1800 ° C., the tap density does not increase any more, and the upper limit temperature of 1800 ° C. is determined for energy saving. Here, the tap density refers to a value obtained by dividing the mass of the particles when the particles are placed in a predetermined container and filled by applying vibration, by the particle volume.

The invention according to claim 5 is the invention according to claim 1 or 2, which is a method for roasting dried insoluble tannin at a temperature of 800 to 1700 ° C. in an argon gas atmosphere. This method is a method for producing nuclear fuel granules in the form of carbides for making pellets. When the insoluble tannin after drying is roasted in an argon gas atmosphere, the tannin component is carbonized and reacts with a nuclear fuel substance such as uranium to form a carbide. When roasting at a temperature in the range of 800 to 1700 ° C., the obtained carbide particles are relatively agglomerated, so that they can be formed into pellets as they are, and the pellets can be sintered into nuclear fuel pellets. . If the roasting temperature is lower than 800 ° C., carbides are not generated, and if the roasting temperature is higher than 1700 ° C., sintering of the particles proceeds. There is a problem that fine powder is generated during pulverization.

The invention according to claim 6 is the invention according to claim 1 or 2, which is a method for roasting dried insoluble tannin at a temperature of 1700 to 2000 ° C. in an argon gas atmosphere. This method is a method of producing nuclear fuel granules in the form of a carbide for producing a filled nuclear fuel. 170
At a temperature of 0 ° C. or higher, the sintering of the particles proceeds, and the particles become particles having a high tap density. Therefore, the particles can be directly filled in a metal tube to be used as nuclear fuel. If the temperature is lower than 1700 ° C., sintering of the particles does not occur and a desired tap density cannot be obtained. If it exceeds 2000 ° C., carbides will decompose.

The invention according to claim 7 is the invention according to claim 1 or 2, which is a method of roasting dried insoluble tannin at a temperature of 1200 to 1700 ° C. in a nitrogen gas atmosphere. This method is a method of producing nuclear fuel granules in the form of a nitride for making pellets. When the insoluble tannin after drying is roasted in a nitrogen gas atmosphere, the tannin component is first carbonized and reacts with a nuclear fuel material such as uranium at a temperature of 800 ° C. or more to produce a carbide, as in the case of the above-mentioned carbide. . Next, the carbide reacts with the nitrogen gas in the atmosphere at a temperature of 1200 ° C. or more to form a nitride. 1200-
When roasting at a temperature in the range of 1700 ° C., the obtained nitride particles are relatively loosely aggregated. Therefore, the particles can be formed into pellet shapes as they are, and the pellets can be sintered into nuclear fuel pellets. If the roasting temperature is lower than 1200 ° C., nitrides are not generated, and if the roasting temperature is higher than 1700 ° C., the sintering of the particles proceeds. There is a problem that fine powder is generated during pulverization.

An eighth aspect of the present invention is the method according to the first or second aspect, wherein the dried insoluble tannin is roasted at a temperature of 1700 to 2000 ° C. in a nitrogen gas atmosphere. This method is a method of producing nuclear fuel granules in the form of a nitride for producing a filled nuclear fuel. 1700 ° C
At the above temperature, the sintering of the particles proceeds, and the particles have a high tap density. Therefore, the particles can be directly filled into a metal tube to be used as nuclear fuel. If the temperature is lower than 1700 ° C., sintering of the particles does not occur and a desired tap density cannot be obtained. If it exceeds 2000 ° C., the nitride will decompose.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous solution containing a nuclear fuel substance of the present invention is an aqueous solution containing one or more of thorium, uranium, plutonium, and other transuranium elements (hereinafter, referred to as uranium). Specifically, it is an aqueous solution containing an element such as uranium such as uranium or plutonium in the form of a compound such as uranyl nitrate or plutonium nitrate and dissolving in water. This aqueous solution is, for example, a nitric acid solution containing uranyl nitrate, plutonium nitrate, and other transuranium elements obtained by reprocessing spent nuclear fuel, or uranyl fluoride generated by hydrolysis of uranium hexafluoride, which is a raw material of uranium fuel. Aqueous solution and the like.

The insoluble tannin of the present invention means a tannin that is insoluble in any of water, acid and alkali.
This insoluble tannin is prepared by dissolving a hydrolyzable tannin powder in aqueous ammonia, adding an aldehyde aqueous solution to the solution to form a precipitate, heating the precipitate, and adding a mineral acid to the heated precipitate. After mixing, it is preferably formed by filtration and drying. As other insoluble tannins, dissolve the condensed tannin powder in an aqueous aldehyde solution,
Ammonia is added to this solution to form a precipitate, and the precipitate is aged. For the insoluble tannin having a particle size of 0.01 to 5 mm used in the present invention, for example, the insoluble tannin obtained by the above method is fractionated through a predetermined mesh sieve.

In order to bring an aqueous solution containing a nuclear fuel substance into contact with an insoluble tannin and adsorb a nuclear fuel substance such as uranium to the insoluble tannin, a method of passing an aqueous solution containing the nuclear fuel substance through a column filled with the insoluble tannin, A method of adding insoluble tannin to an aqueous solution containing the solution and filtering the solution to recover the insoluble tannin having adsorbed the nuclear fuel substance is adopted. When considering the continuity of the process,
The former method is preferred. In order to compress and dehydrate the swollen insoluble tannin by adsorbing the nuclear fuel material, a method of passing the swollen tannin between two rolls which are opposed to each other and rotate in opposite directions, or a method using a hydraulic press Etc. are adopted. When the continuity of the process is considered, the former method is preferable.

The drying of the insoluble tannin which has been dehydrated by compression is performed by
It is performed in a temperature range from room temperature to 400 ° C. If the drying is insufficient, particles of nuclear fuel material such as uranium are easily broken at the time of roasting, and there is a disadvantage that fine powder is generated. If the drying temperature is lower than room temperature, it takes too much time for drying, which is inconvenient. If it exceeds 400 ° C., the particles of the nuclear fuel material are easily broken by rapid evaporation of water, and fine powder is easily generated at that time. The roasting process decomposes or burns the tannin component in the insoluble tannin after drying into carbon, hydrogen, or oxygen, and converts the nuclear fuel material component into an oxide, carbide, or nitride that is a stable chemical form that can be used as nuclear fuel. This is a necessary step. In order to make oxides, carbides or nitrides, it is necessary to change the atmosphere and the roasting temperature as described above.
The roasting time varies depending on the amount of insoluble tannin, but is about 10 minutes to 10 hours.

When obtaining nuclear fuel granules in the form of carbides,
The amount of carbon obtained by carbonization of tannin is an amount sufficient to reduce and carbonize metal components such as uranium, and is exclusively excessive. This excess carbon can be removed in the form of a gas such as methane by adding hydrogen to the atmosphere (methanation reaction). When the particles are dispersed in a carbon matrix and used as a so-called fuel compact, for example, in a high-temperature gas furnace, there is no need to remove the carbon.

[0018]

EXAMPLES Next, examples of the present invention will be described together with comparative examples in order to show specific embodiments of the present invention. <Example 1> Particle size is 0.01 to 5 mm (average particle size is about 1
mm) of insoluble tannin (trade name: Tannics, manufactured by Mitsubishi Nuclear Fuel Co., Ltd.) and a uranium concentration of 3% by weight and a pH of 3
(Uranyl nitrate aqueous solution) was prepared.
500 ml of the aqueous solution having a temperature of 25 ° C. was stored in a container, and 700 g of the insoluble tannin (about 150 g in dry weight) was added to the aqueous solution, and the mixture was stirred for about 1 hour to adsorb the uranium component to the insoluble tannin. After removing the insoluble tannin to which the uranium component was adsorbed from the container, the uranium component was compressed and dehydrated through the insoluble tannin swollen between two rolls facing and separated from each other and rotating in opposite directions until the water content became 40%.

The insoluble tannin which had been dehydrated by compression was dried at 200 ° C. for 1 hour and then calcined at 800 ° C. for 2 hours in an oxygen atmosphere. The insoluble tannin was burned off by roasting, and porous granules having a particle size of 0.01 to 4 mm were obtained. The average particle size of the granules was about 0.7 mm. When the granules were analyzed by X-ray diffraction, they were uranium oxides.

Example 2 Porous granules composed of uranium oxide were obtained in the same manner as in Example 1 except that an aqueous solution having the same uranium concentration as in Example 1 and a pH of 4 was used.

Comparative Example 1 Porous granules made of uranium oxide were obtained in the same manner as in Example 1 except that an aqueous solution having the same uranium concentration as in Example 1 and a pH of 2 was used.

<Comparative Test> The uranium concentration in each of the aqueous solutions of Examples 1 and 2 and Comparative Example 1 remaining in the container from which the swollen insoluble tannin was removed was determined, and the adsorption rate α of the insoluble tannin was determined by the following equation. . Table 1 shows the results. α = [(Co-Ct) / Co] × 100 (%) where Co is the uranium concentration in the aqueous solution before adding the insoluble tannin, and Ct is the uranium concentration in the aqueous solution after removing the insoluble tannin.

[0023]

[Table 1]

The uranium adsorption rate of the insoluble tannin was 3.8% in Comparative Example 1 with a pH of 2, whereas 93.2% and 9 in Examples 1 and 2 with a pH of 3 and 4, respectively.
8.0%, which indicates that Examples 1 and 2 can produce nuclear fuel granules more efficiently.

<Embodiment 3> In an argon gas atmosphere, 16
Porous granules having a particle size of 0.01 to 4 mm were obtained in the same manner as in Example 1 except that the mixture was roasted at 00 ° C. for 4 hours and then excess carbon was removed by a methanation reaction in a hydrogen atmosphere. The average particle size of the granules was about 0.6 mm. The granules were analyzed by the same analyzer as in Example 1 and found to be uranium carbide.

Example 4 1600 in a nitrogen gas atmosphere
The resulting mixture was roasted at 4 ° C. for 4 hours, and then subjected to a methanation reaction in a hydrogen atmosphere to remove excess carbon, thereby obtaining porous granules having a particle size of 0.01 to 4 mm in the same manner as in Example 1. The average particle size of the granules was about 0.6 mm. The granules were analyzed by the same analyzer as in Example 1 and found to be uranium nitride.

[0027]

As described above, according to the present invention, an aqueous solution containing a nuclear fuel substance is brought into contact with an insoluble tannin having a predetermined particle size to adsorb the nuclear fuel substance to the insoluble tannin, and the insoluble tannin having the nuclear fuel substance adsorbed thereon is produced. After compression dehydration, drying, and roasting, a granular nuclear fuel in which insoluble tannin has been burnt out can be obtained. If pellets or filled fuel are produced from the nuclear fuel granules, the granules will not be scattered as fine powder during the production process. In addition, since compression dehydration, drying, and roasting are performed, an effect of reducing energy consumption required for production can be obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // C07G 17/00 C07G 17/00 A (56) References JP-A-5-50058 (JP, A) JP-A 5- 66291 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21F 9/06 G21C 19/46

Claims (8)

(57) [Claims] 1. A method for producing nuclear fuel by bringing an aqueous solution containing a nuclear fuel substance into contact with insoluble tannin to cause the nuclear fuel substance to be adsorbed on the insoluble tannin, and then baking the insoluble tannin adsorbing the nuclear fuel substance. Has a particle size of 0.01 to 5 mm, the aqueous solution contains 1 to 10% by weight of nuclear fuel material, and after insoluble tannin adsorbing the nuclear fuel material is compressed and dehydrated, dried at room temperature to 400 ° C. And baking the dried insoluble tannin in an oxidizing atmosphere or a non-oxidizing atmosphere at a temperature of 400 to 2000 ° C., to produce nuclear fuel granules using insoluble tannin. 2. The nuclear fuel granules using insoluble tannin according to claim 1, wherein the aqueous solution containing a nuclear fuel substance is a uranium compound aqueous solution having a uranium concentration of 1 to 10% by weight, and the pH of the aqueous solution is 3 to 4. Production method. 3. The method for producing nuclear fuel granules using insoluble tannin according to claim 1, wherein the dried insoluble tannin is roasted in an oxidizing atmosphere at a temperature of 400 to 800 ° C. 4. The method according to claim 1, wherein the dried insoluble tannin is roasted in an oxidizing atmosphere at a temperature of 800 to 1800 ° C.
A method for producing nuclear fuel granules using the insoluble tannin according to the above. 5. The method for producing nuclear fuel granules using insoluble tannin according to claim 1, wherein the dried insoluble tannin is roasted at a temperature of 800 to 1700 ° C. in an argon gas atmosphere. 6. The method for producing nuclear fuel granules using insoluble tannin according to claim 1, wherein the dried insoluble tannin is roasted at a temperature of 1700 to 2000 ° C. in an argon gas atmosphere. 7. The dried insoluble tannin is roasted at a temperature of 1200 to 1700 ° C. in a nitrogen gas atmosphere.
Or a method for producing nuclear fuel granules using the insoluble tannin according to 2. 8. The method according to claim 1, wherein the dried insoluble tannin is roasted at a temperature of 1700 to 2000 ° C. in a nitrogen gas atmosphere.
Or a method for producing nuclear fuel granules using the insoluble tannin according to 2.